Cathode ray tube having multiple field emission cathodes

ABSTRACT

Apparatus and method are provided for using a multi-element field emission cathode in a color cathode ray tube. The field emission cathode may have from four to ten field emission arrays linearly arranged. The arrays are preferably formed from carbon-based material. An electron gun assembly focuses electron beams from each array on to a phosphor stripe or dot on the screen of the cathode ray tube. Deflection apparatus moves the beam from each field emission array according to clock signals. Clock signals also turn on or turn off voltage to contacts controlling electron current from the array. Values of voltage applied, determined by a video signal, determine the intensity of electron current from each array, which controls the intensity of the light emitted by each color stripe or dot of phosphor on the phosphor screen.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to cathode ray tubes. More particularly,the invention relates to an array of independently modulated electronbeams emanating from field emission cathodes in a cathode ray tube.

[0003] 2. Description of Related Art

[0004] Higher brightness and simpler construction have long been thegoal of manufacturers of cathode ray tubes (“CRTs”). In commercial CRTs,brightness is limited by the electron gun current that can be extractedfrom a thermionic cathode and passed through a small aperture. The smallaperture is required to restrict the electron source size and produce asmall spot of light on a phosphor screen.

[0005] Another limitation on brightness of cathode ray tubes arises fromthe use of a shadow mask. The shadow mask is effectively a limitingaperture for the electron beam near the plane of the CRT screen. Itnormally captures from about 30 to 80 percent of the incident electronbeam and reduces image brightness by a corresponding amount. Eliminationof the shadow mask could regain this lost electron beam current andthereby increase image brightness. Elimination of the shadow mask wouldalso reduce complexity of CRT manufacturing and thereby reduce cost.

[0006] Replacing the thermionic oxide cathode with a field emission (FE)cathode can increase electron current and brightness because the FEcathode can deliver a higher current density per unit area. Use ofcarbon-based FE cathodes in electron guns of CRTs has been disclosed incommonly assigned and co-pending application S.N. 09/169,908, filed Oct.12, 1998 and in U.S. Pat. No. 6,181,055B1, which are hereby incorporatedby reference herein. Still, even with a FE cathode, a brightnessincrease by a factor of two or three above an oxide cathode CRT is aboutthe limit of achievability. This limitation is primarily caused byexcessive space charge and phosphor power-dissipation limitations.

[0007] There is a significant quantity of prior art relating to multipleelectron beams in CRTs. Most of the prior art is meant for use withthermionic cathodes. For example, U.S. Pat. Nos. 3,943,281, 4,954,901and 5,557,344 disclose multiple-beam, multiple-raster CRTs that have aplurality of controllable cathodes that are oriented vertically. Eachbeam is directed to scan a separate scan line and is separatelymodulated, so that the horizontal scan rate can be reduced by a factorequal to the number of beams. This results in increased framebrightness. These patents all disclose a system requiring a shadow mask.U.S. Pat. No. 5,585,691 describes a method for changing video signaltiming in order to provide dynamic color separation and remove the needfor a shadow mask in a CRT. The method uses complicated electronics andis limited to specific applications.

[0008] There is a need for improved apparatus and method for increasingthe brightness, obtaining better spot resolution, allowing instantaneouselectronic beam turn-on and eliminating the requirement for a shadowmask in cathode ray tubes. Reductions in complexity and cost ofmanufacturing are also needed.

SUMMARY OF THE INVENTION

[0009] Toward providing these and other advantages, apparatus and methodare provided for a cathode ray tube having a field emission cathode andeliminating the requirement for a shadow mask.

[0010] In one embodiment, a cathode ray tube having a multi-elementcathode is provided. The multi-element cathode has several arrays offield emission cathodes aligned on a common carrier assembly. The arraysare preferably formed from carbon-based material. An electron gunfocuses the electron beam from each array on to the phosphor screen ofthe cathode ray tube.

[0011] In another embodiment, a multi-element cathode is provided. Inyet another embodiment, method for forming an image on the screen of acathode ray tube using a multi-element field emission cathode isprovided. An electronic circuit to allow scanning electron beams to forman image is also provided.

DESCRIPTION OF THE FIGURES

[0012] For a more complete understanding of the invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the following drawings in which like referencenumbers indicate like features and wherein:

[0013]FIG. 1 shows the top view of a cathode ray tube having amulti-element field emission cathode.

[0014]FIG. 2 shows the front view of a multi-element field emissioncathode.

[0015]FIG. 3 shows a diagram of a horizontal sweep across a CRT screenillustrating variations in electron beam current with clock signals.

[0016]FIG. 4 shows a thin mask stripe deposited in the boundary betweeneach phosphor stripe to increase color separation.

[0017] FIGS. 5(a) and 5(b) show a diagram of an electronic circuit toaccomplish the timing of an electron beam to create a color image.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0018] Referring to FIG. 1, the top view of a cathode ray tube having afield emission cathode is shown generally at 10. Multi-element fieldemission cathode 20 is at the source end of electron gun assembly 12.Gun assembly 12 is located inside the neck of envelope 17. Multi-elementfield emission cathode 20 will be described in more detail below. Theseelectrodes comprising the gun assembly are operated at independentpotentials such that electrons emitted from the plane of the cathodearray are imaged on to phosphor screen 19. The electron gun elementscombine to form the equivalent of a single optical lens that maps theelectron field emission site at specific positions on the cathode arrayinto an image of the array on the screen, modified only by themagnification of the electron optics and any aberration or otherimperfections in the imaging. Methods for calculating such imaging ofelectron sources and electron beams are known, and are discussed, forexample, in commonly assigned application S.N. 09/356,851, filed Jul.19, 1999, which is hereby incorporated by reference herein. Since fieldemission is constrained to emanate from only the linear array of cathodeelements, the electron optics reproduces this linear array on to screen19. Multiple cathode elements in the linear array form a correspondingmultitude of bright spots on the screen such as shown at 18.

[0019] Phosphor on the screen in a color CRT is normally divided intored, green and blue (RGB) dots. A phosphor dot is typically about 200micrometers in diameter, but may be larger or smaller, depending on theresolution of the CRT. Higher resolution monitors for television or forother purposes may use smaller phosphor dots. Bright spots on phosphordots correspond to spots 18 illustrated on phosphor screen 19.Deflection apparatus 11 is used to cause the electron beams to traversethe span of the screen in both horizontal and vertical directions,forming a rectangular video image for each full cycle of traversal.Color information is normally imparted to the image by the RGB phosphorsin adjacent alternating spots or stripes on the inside of the CRT screen19. Modulation of the electron beam current in a fashion that issynchronized with the color phosphor locations produces a color image.

[0020] Referring to FIG. 2, a linear field emission array is generallyshown at 20. The array may include individual cathode subassemblies 22mounted on common carrier assembly 21. Each of the cathode subassembliesin the array includes two bond pads: field emitting material pad 23 andgate electrode pad 24. Electrons emitted by the field emitting materialemanate from a plurality of individual sites 25 within active area 26 ofthe cathode subassembly. Any field emission array, including an array ofSpindt tips, may be used according to the apparatus and methodsdisclosed here. A preferred field emitting array is formed from a carbonbased material disclosed in S.N. 169,908, filed Oct. 12, 1998 and U.S.Pat. No. 6,181,055B1, referenced above, each of which is incorporated byreference herein. The emission current from each cathode subassembly iscontrolled by application of voltage between contacts or bond pads 23and 24, with emission current increasing with increasing positivevoltage on gate electrode 24 with respect to field emitting material pad23. The spacing between the individual active areas of each cathodesubassembly 22 is precisely controlled during assembly. Duringoperation, the field emission current from each of cathode subassemblies22 is independently controlled, forming distinct electron beams thatpropagate in a direction normal to the plane of cathode 20. The diameterof each active area 26 is normally in the range of about 10 to about 100micrometers, but larger or smaller active areas may be used. The smallerarea will be limited by the number of active emitters within each areaand larger area will be limited by the total span of the multiplecathodes. The length of subassembly 22 is typically in the range ofabout 70 micrometers, but it may be larger or smaller. Preferably sixactive areas are used as a cathode in a color CRT. Any number of activeareas may be used, limited by the total overall dimension and theability to image extended sources.

[0021]FIG. 3(a) illustrates images of the active areas of cathodesubassemblies as they would appear on the screen of a CRT. Theindividual electron beams may impinge upon the phosphor in a set ofoverlapping regions, with each beam creating a luminous spot on the CRTscreen that has the hue of the corresponding phosphor material and aluminosity proportional to the value of electron beam current.Variations of electron beam current as the beam is swept across thescreen of a CRT are illustrated in FIG. 3(b). The array of overlappingregions is oriented in the same direction (shown to be horizontal) asthe array of cathode subassemblies on the field emission cathode. Theremay be a 1:1 correspondence between the dimensions of the cathodeemission areas 26 and the overlapping regions on the screen, or thedimensions of the cathode may be changed by an overall magnificationfactor. The cathode images may also exhibit blurring or other aberrationfrom the electron optics. For example, the stripes of red, green andblue phosphor as shown in FIG. 3 may have widths of about 50-100microns. The image of the cathode subassemblies 34 may have a diameterin the range of about 25-50 microns. Preferably, the spot diameter isabout one-half of the phosphor stripe width. Smaller spot sizes are moreexpensive to produce and the corresponding higher bandwidths requiredfor current modulation is more expensive as well. In the presentinvention, the deflection apparatus causes the array of overlappingelectron beams to traverse the surface of the screen together, each beamexciting the phosphor it impinges upon proportionally to that beam'scurrent. The beam strikes red phosphor 30, green phosphor 31 and bluephosphor 32, which may be arranged in vertical stripes. If theindividual electron beam's impingement area 33 is approximately half thewidth of the phosphor stripe, and the modulation of the electron beam'scurrent is controlled precisely in synchronization with the horizontaldeflection apparatus, then an embodiment of a color CRT is realized.

[0022] FIGS. 3(b) and 3(c) illustrate clock signal 35 and electron beamcurrent 37, which corresponds to movement of the electron beam acrossstripes of phosphor as shown in FIG. 3A. Following the array of electronbeams through a horizontal sweep across the CRT screen, at time zero,defined by the rising edge of a clock signal 35 (FIG. 3(c)), first beam34 (FIG. 3(a)) is positioned at the boundary of the red phosphor stripe30. At this instant, the first electron beam's current is selected toassume a value proportionate to the red component of the first pictureelement in the current horizontal scan line, I_(P1R). All of the otherelectron beams may be selected to have zero current. Later, at time 1,defined by the second rising edge of clock signal 35, the array ofelectron beams has moved together a distance of one-half an individualbeam width. This causes the first electron beam to move fully into thered phosphor stripe and it is still commanded to output current I_(P1R).The second electron beam is now also commanded to output currentI_(P1R). After another clock increment, at time 2, the third electronbeam is commanded to output current I_(P1R), along with the first andsecond electron beams. At clock phase 3, shown in FIG. 3(a), the edge ofthe first electron beam has reached the boundary between the red andgreen phosphor and is commanded to zero current, while the second, thirdand now fourth electron beams are commanded to current I_(P1R). At thebeginning of the next time interval, the first electron beam is centeredon the boundary between red and green phosphors and is now commanded tocurrent I_(P1G), the current proportional to the green component of thefirst picture element's luminosity. The time is denoted time zero orclock phase zero again, because it marks the beginning of a four-periodinterval in which the first electron beam is commanded to a selectedcurrent, at the end of which its current is commanded to a value ofzero.

[0023] It should be clear that for the preferred spot size 12 periods ofclock phase are required for each picture element, 4 periods for eachphosphor color, and that during 3 of those periods the electron beam iscommanded to emit a non-zero current. Because of the finite bandwidth ofthe video driver and cathode combination, the actual electron beamcurrent 37 will lag the commanded value of current 36 (FIG. 3(b))somewhat and will not be able to track the sharp transitions between thecommanded values. The video bandwidth must be at least high enough sothat the actual electron beam current falls to a small value somewherein the interval between time 3 and the following time zero in order tominimize bleed-over between adjacent colors.

[0024] In another embodiment, shown in FIG. 4, thin mask stripe 40 isdeposited at the boundary between each phosphor stripe 30, 31 and 32.Mask stripe 40 can be used to increase color separation and furtherdecrease bleed-over between adjacent colors. Stripe 40 may be producedlithographically, using standard techniques. It may be formed of ametal. It may be laid down at the same time the phosphor is deposited.The width of stripe 40 will be related to the bandwidth of the video andpreferably will be approximately one-half the distance that is requiredto turn off the electron beam at sweep velocity.

[0025] An electronic circuit to accomplish the timing of the electronbeams from multi-element cathode 20 of FIG. 1 is shown in FIGS. 5(a) and5(b). The information required to create the color image may becontained in three banks of video memory 501 a, 501 b, and 501 c,corresponding to the red, green, and blue components of the image,respectively. In each bank of memory, there is a memory location,corresponding to each picture element displayed on the screen, thatcontains a digital value representing the intensity of the particularcolor of the particular picture element, i.e., color picture elementintensity. Generally, video picture information is stored into thememory from a video source (502) at a rate that may or may not besynchronized with the display rate, though address (503) and data (504)signals may be separate from those used for the display (505 and 506).Clock generator 507 (FIG. 5(b)) is used to generate the overall timingsignals necessary to drive the display, including the horizontal andvertical synchronization pulses for the deflection drivers and thesource of the video master clock (CLK). The frequency of the clockgenerator is controlled by quartz crystal 508 to ensure the accurateinterval timing necessary for synchronization.

[0026] The CLK signal from the clock generator 507 is supplied to adivide-by-four counter 509 having carry output 511 and also to wordshift register 510, which comprises five load registers. Thedivide-by-four counter 509 counts in succession values 0-3, in time withfour successive clock pulses, before resetting to 0 and outputting carrysignal 511 on line INCCOLOR. The divide-by-four counter counts 0-3,denoted by PHASE; 0, 1, 2, and 3 correspond to the respective CLKintervals in FIG. 3. The INCCOLOR signal is input to divide-by-threecounter 512 that counts 0-2 before resetting to 0 and out-putting acarry signal 513 on line INCPIXEL. The state of the divide-by-threecounter, denoted by COLOR, is fed to 1-of-3 digital word multiplexer517, which is used to select one of the three color-related intensityvalues. These intensity values come from the three memory banks 501 a,501 b, and 501 c, one word for each color, and are individuallygamma-corrected in word multipliers 516, 515, and 514. The specificpicture element being displayed is selected by address counter 505,which is common to all three video memory banks 501 a, 501 b, 501 c.

[0027] The output from color multiplexer 517 is fed to 2-of-1multiplexer 518 that selects whether to simply pass the digitalinformation through or to set it to zero, depending upon the state ofthe PHASE counter 509.

[0028] AND gate 519 switches the state of gate multiplexer 518 only whenthe PHASE counter is in state 3, which provides the means for turningoff the electron beam when it crosses a phosphor color-boundary. Theoutput of gate multiplexer 518 is the digital intensity word for thefirst electron beam. This digital value is sent to digital-to-analogconverter 520, which comprises six digital-to-analog converter modules.The first module of digital-to-analog converter 520 converts the digitalcommand into a voltage 521 that is used to control the gate electrode ofthe cathode subassembly for electron beam one. The second module ofdigital-to-analog converter 520 is connected to the first load registerof shift register 510, the third module connected to the second loadregister, and so on. Every rising edge of the CLK signal causes theshift register 510 to shift the digital command for electron beam oneinto the signal that carries the digital command for electron beam two.Similarly, beam two's command is shifted to beam three, and so on. Thenet effect is that as the linear array of electron beams traverse theCRT screen, the commanded value for a given phosphor stripe in a givenpicture element is supplied to whichever electron beam is currentlyilluminating that phosphor stripe.

[0029] Reset signals are used to start the electronics in a known stateat the beginning of each vertical frame and each horizontal sweep line.Signal RA (FIG. 5a) is generated to reset the video memory address atthe beginning of a frame. Signal RS (FIG. 5b) resets and clears all ofthe digital outputs in the shift register 510 prior to a horizontalsweep. Signal RC (FIG. 5a) resets the PHASE 509 and COLOR 512 countersto state 0 at the beginning of each horizontal line.

[0030] The disclosed CRT has increased brightness because of themultiple sources of electron beams and the lack of a shadow mask. Thefield emission cathodes can be energized instantaneously, and the colorconvergence adjustment is based solely on electronic timing. The smallfield emission cathodes have smaller capacitance and thus a higher videobandwidth capability than the thermionic cathodes of conventional CRTs.This allows the electron beams to be turned on and off faster whencrossing phosphor boundaries. This will decrease the need for a shadowmask in the CRT, which is expensive to install during manufacture.According to the present disclosure, phosphor can be printed directlyonto the inside face of the CRT screen 19 (FIG. 1), instead of beingdeposited in precise alignment with a shadow mask. The multiple electronbeams means that each separate beam can have a smaller current and theviewer sees the effect of the total current from all the beams. Thus,each cathode is smaller and has a lower capacitance. Failure of a smallnumber of cathode subassemblies results in an overall intensity decreaseof 1/N, where N is the total number of cathodes in the assembly.

[0031] In one embodiment, dynamic beam focus during sweep is employed.In another embodiment, dynamic timing adjustment is employed at largedeflection angles.

[0032] Methods for beam adjustment using distortion correction circuitsare well known, and are described, for example, in the book VideoEngineering, by A. Luther et al, Mc-Graw-Hill, 1999, pp. 5-39 through5.45, which are hereby incorporated by reference.

[0033] While preferred embodiments of the invention have been described,it should be understood that one of ordinary skill in the art mayrecognize other embodiments of the invention, and that the invention islimited only by the appended claims.

What we claim is:
 1. A cathode ray tube, comprising: an envelope havinga neck and a phosphor screen; an electron gun assembly having a sourceend and electrodes for focusing an electron beam, the electron gun beingdisposed in the neck; a multi-element field emission cathode disposed atthe source end of the electron gun assembly; and deflection apparatus tocause the electron beam from the multi-element field emission cathode totraverse the phosphor screen in a horizontal and a vertical direction.2. The cathode ray tube of claim 1 wherein the multi-element fieldemission cathode comprises a plurality of individual cathodesub-assemblies on a common carrier, each of the individualsub-assemblies having contacts for controlling field emission electricalcurrents.
 3. The cathode ray tube of claim 1 wherein the multi-elementfield emission cathode is formed from carbon-based material.
 4. Thecathode ray tube of claim 2 wherein the number of subassemblies is inthe range from four to ten.
 5. The cathode ray tube of claim 2 whereinthe number of subassemblies is six.
 6. The cathode ray tube of claim 1wherein the phosphor screen is comprised of a plurality of stripes ofphosphor.
 7. The cathode ray tube of claim 6 further comprising aplurality of stripes of mask material disposed between the plurality ofstripes of phosphor.
 8. A multi-element field emission cathode,comprising: a common carrier assembly; and a plurality of sub-assemblieson the common carrier assembly, each sub-assembly having a fieldemission array, the array having a selected area and electrical bondpads for controlling emission current from the array.
 9. The fieldemission cathode of claim 8 wherein the field emission array iscomprised of carbon-based emitters.
 10. The field emission cathode ofclaim 8 wherein the selected area of the array is circular, the areahaving a diameter in the range from about 10 micrometers to about 100micrometers.
 11. The field emission cathode of claim 8 wherein the widthof a sub-assembly is approximately 70 micrometers.
 12. The fieldemission cathode of claim 8 wherein the number of sub-assemblies mountedon the common carrier assembly is in the range from four to ten.
 13. Thefield emission cathode of claim 8 wherein the number of sub-assembliesmounted on the common carrier assembly is six.
 14. A method for formingan image on a phosphor screen of a cathode ray tube, comprising:providing an electron gun assembly having an electron source disposed ata source end and electrodes for forming an image of the electron sourceon the phosphor screen; providing a multi-element field effect cathodeto serve as the electron source, the multi-element field effect cathodecomprising a common carrier assembly and a plurality of field emissionarrays and electrical bond pads for controlling emission current fromeach array; providing a deflection apparatus to cause an electron beamfrom each array to traverse the phosphor screen in a horizontal and avertical direction. providing a clock signal having a selected number ofsuccession of increments; and applying selected voltages to thedeflection apparatus and to the electrical bond pads in response to theclock signal to cause a selected emission current from a selected arrayas the electron beam from the array traverses the phosphor screen. 15.The method of claim 14 wherein an increment of the clock signal causesthe electron beam to move a distance of one-half the width of the beam.16. The method of claim 14 wherein four increments of the clock signalcause the electron beam to move across a phosphor stripe having aselected color.
 17. The method of claim 14 wherein the field emissionarray is a carbon-based material.
 18. An electronic circuit forcontrolling electron beams from a plurality of field emission cathodesto produce a color image from a television signal onto a phosphor screenof a cathode ray tube (CRT), comprising: a video memory adapted toreceive and store color video information from a video source, the colorvideo information comprising red, green and blue intensity values foreach spot to be illuminated on a cathode ray tube (CRT) having aplurality of substantially vertical red, green and blue phosphorstripes, wherein adjacent portions of the red, green and blue phosphorstripes comprise the spots to be illuminated; the video memory havingaddressable first, second and third memory portions for storing the red,green and blue intensity values, respectively, wherein the red, greenand blue intensity values for a spot are stored at the samecorresponding address of the first, second and third memory portions,respectively; an address counter for selecting memory addressescorresponding to spot locations on the CRT face, the address countercoupled to the video memory; a color multiplexer having first, secondand third inputs coupled to the first, second and third memory portions,respectively, and an output; a color counter coupled to and controllingthe color multiplexer for selecting the red, green and blue intensityvalues from the video memory, wherein the color counter increments theaddress counter after each selection sequence of red, green and blueintensity values; a gate multiplexer have a first input, a second inputand an output, the gate multiplexer first input coupled to the colormultiplexer output, and the gate multiplexer second input set to a zerointensity value; a phase counter coupled to and controlling the gatemultiplexer, wherein the phase counter switches the gate multiplexeroutput to the second input having the zero intensity value at eachfourth phase count; an intensity value shift register adapted forreceiving intensity values from the gate multiplexer and storing thereceived intensity values in sequential order, the intensity value shiftregister comprising a plurality of registers, wherein an input of afirst one of the plurality of registers is connected to the output ofthe gate multiplexer and remaining ones of the plurality of registerseach have an output connected to an input of a subsequent one until thesubsequent one is a last one of the plurality of registers; a pluralityof digital-to-analog converters (DACs), each of the plurality of DACshaving an output adapted for coupling to a respective one of a pluralityof field emission cathodes; a first one of the plurality of DACs havingan input coupled to the output of the gate multiplexer, and an input ofeach of the remaining ones of the plurality of DACs being connected tothe output of respective ones of the plurality of registers; and a videoclock having an output coupled to the phase counter and the intensityvalue shift register, wherein the video clock times when the red, greenand blue intensity values for each spot and the zero intensity valuebetween adjacent spots are applied through the plurality of fieldemission cathodes to the spot portions of the phosphor stripes of theCRT.
 19. The apparatus of claim 18, wherein each of the plurality ofregisters can store an eight bit intensity value.
 20. The apparatus ofclaim 18, further comprising: first, second and third multipliers forgamma correcting the red, green and blue intensity values, respectively;and the first, second and third multipliers coupled between the first,second and third memory portions and the first, second and third inputsof the color multiplexer.
 21. The apparatus of claim 18, wherein thenumber of the plurality of DACs is selected from the group consisting of2, 3, 4, 5, 6, 7, 8, 9 and
 10. 22. The apparatus of claim 18, whereinthe number of the plurality of registers is selected from the groupconsisting of 2, 3, 4, 5, 6, 7, 8, 9 and
 10. 23. An electronic circuitfor controlling electron beams from a plurality of field emissioncathodes to produce a color image from a television signal onto aphosphor screen of a cathode ray tube (CRT), comprising: a colormultiplexer adapted for receiving color video information comprisingred, green and blue intensity values, the color multiplexer havingfirst, second and third inputs adapted for receiving the red, green andblue intensity values, respectively; a color counter coupled to andcontrolling the color multiplexer for selecting the red, green and blueintensity values; a gate multiplexer have a first input, a second inputand an output, the gate multiplexer first input coupled to the colormultiplexer output, and the gate multiplexer second input set to a zerointensity value; a phase counter coupled to and controlling the gatemultiplexer, wherein the phase counter switches the gate multiplexeroutput to the second input having the zero intensity value at eachfourth phase count; an intensity value shift register adapted forreceiving intensity values from the gate multiplexer and storing thereceived intensity values in sequential order, the intensity value shiftregister comprising a plurality of registers, wherein an input of afirst one of the plurality of registers is connected to the output ofthe gate multiplexer and remaining ones of the plurality of registerseach have an output connected to an input of a subsequent one until thesubsequent one is a last one of the plurality of registers; a pluralityof digital-to-analog converters (DACs), each of the plurality of DACshaving an output adapted for coupling to a respective one of a pluralityof field emission cathodes; a first one of the plurality of DACs havingan input coupled to the output of the gate multiplexer, and an input ofeach of the remaining ones of the plurality of DACs being connected tothe output of respective ones of the plurality of registers; and a videoclock having an output coupled to the phase counter and the intensityvalue shift register, wherein the video clock times when the red, greenand blue intensity values for each spot and the zero intensity valuebetween adjacent spots are applied through the plurality of fieldemission cathodes to the spot portions of the phosphor stripes of theCRT.
 24. The apparatus of claim 23, wherein each of the plurality ofregisters can store an eight bit intensity value.
 25. A method forcontrolling electron beams from a plurality of field emission cathodesto produce a color image from a television signal onto a phosphor screenof a cathode ray tube (CRT), the method comprising the steps of:providing a video memory adapted to receive and store color videoinformation from a video source, the color video information comprisingred, green and blue intensity values for each spot to be illuminated ona cathode ray tube (CRT) having a plurality of substantially verticalred, green and blue phosphor stripes, wherein adjacent portions of thered, green and blue phosphor stripes comprise the spots to beilluminated; storing the red, green and blue intensity values intofirst, second and third addressable memory portions, respectively, ofthe video memory; selecting memory addresses corresponding to spotlocations on the CRT face with an address counter; providing a colormultiplexer having first, second and third inputs coupled to the first,second and third memory portions, respectively, and an output; selectingthe red, green and blue intensity values from the video memory with acolor counter coupled to and controlling the color multiplexer, whereinthe color counter increments the address counter after each selectionsequence of red, green and blue intensity values; providing a gatemultiplexer have a first input, a second input and an output, the gatemultiplexer first input coupled to the color multiplexer output, and thegate multiplexer second input set to a zero intensity value; providing aphase counter coupled to and controlling the gate multiplexer, whereinthe phase counter switches the gate multiplexer output to the secondinput having the zero intensity value at each fourth phase count;providing an intensity value shift register adapted for receivingintensity values from the gate multiplexer and storing the receivedintensity values in sequential order, the intensity value shift registercomprising a plurality of registers, wherein an input of a first one ofthe plurality of registers is connected to the output of the gatemultiplexer and remaining ones of the plurality of registers each havean output connected to an input of a subsequent one until the subsequentone is a last one of the plurality of registers; providing a pluralityof digital-to-analog converters (DACs), each of the plurality of DACshaving an output adapted for coupling to a respective one of a pluralityof field emission cathodes; wherein a first one of the plurality of DACshaving an input coupled to the output of the gate multiplexer, and aninput of each of the remaining ones of the plurality of DACs beingconnected to the output of respective ones of the plurality ofregisters; and providing a video clock having an output coupled to thephase counter and the intensity value shift register, wherein the videoclock times when the red, green and blue intensity values for each spotand the zero intensity value between adjacent spots are applied throughthe plurality of field emission cathodes to the spot portions of thephosphor stripes of the CRT.
 26. A system having an electronic circuitfor controlling electron beams from a plurality of field emissioncathodes to produce a color image from a television signal onto aphosphor screen of a cathode ray tube (CRT), the system comprising: avideo memory for receiving and storing color video information from avideo source, the color video information comprising red, green and blueintensity values for each spot to be illuminated on a cathode ray tube(CRT) having a plurality of substantially vertical red, green and bluephosphor stripes, wherein adjacent portions of the red, green and bluephosphor stripes comprise the spots to be illuminated; the video memoryhaving addressable first, second and third memory portions for storingthe red, green and blue intensity values, respectively, wherein the red,green and blue intensity values for a spot are stored at the samecorresponding address of the first, second and third memory portions,respectively; an address counter for selecting memory addressescorresponding to spot locations on the CRT face, the address countercoupled to the video memory; a color multiplexer having first, secondand third inputs coupled to the first, second and third memory portions,respectively, and an output; a color counter coupled to and controllingthe color multiplexer for selecting the red, green and blue intensityvalues from the video memory, wherein the color counter increments theaddress counter after each selection sequence of red, green and blueintensity values; a gate multiplexer have a first input, a second inputand an output, the gate multiplexer first input coupled to the colormultiplexer output, and the gate multiplexer second input set to a zerointensity value; a phase counter coupled to and controlling the gatemultiplexer, wherein the phase counter switches the gate multiplexeroutput to the second input having the zero intensity value at eachfourth phase count; an intensity value shift register adapted forreceiving intensity values from the gate multiplexer and storing thereceived intensity values in sequential order, the intensity value shiftregister comprising a plurality of registers, wherein an input of afirst one of the plurality of registers is connected to the output ofthe gate multiplexer and remaining ones of the plurality of registerseach have an output connected to an input of a subsequent one until thesubsequent one is a last one of the plurality of registers; a pluralityof digital-to-analog converters (DACs), each of the plurality of DACshaving an output coupled to a respective one of a plurality of fieldemission cathodes; a first one of the plurality of DACs having an inputcoupled to the output of the gate multiplexer, and an input of each ofthe remaining ones of the plurality of DACs being connected to theoutput of respective ones of the plurality of registers; and a videoclock having an output coupled to the phase counter and the intensityvalue shift register, wherein the video clock times when the red, greenand blue intensity values for each spot and the zero intensity valuebetween adjacent spots are applied through the plurality of fieldemission cathodes to the spot portions of the phosphor stripes of theCRT.
 27. The system of claim 26, wherein each of the plurality ofregisters can store an eight bit intensity value.
 28. The system ofclaim 26, further comprising: first, second and third multipliers forgamma correcting the red, green and blue intensity values, respectively;and the first, second and third multipliers coupled between the first,second and third memory portions and the first, second and third inputsof the color multiplexer.
 29. The system of claim 26, wherein the numberof the plurality of DACs is selected from the group consisting of 2, 3,4, 5, 6, 7, 8, 9 and
 10. 30. The system of claim 26, wherein the numberof the plurality of registers is selected from the group consisting of2, 3, 4, 5, 6, 7, 8, 9 and 10.